This invention relates to spark plug printing machines
Spark plugs are usually marked to indicate the manufacturer, type and so on by printing on the insulator body between the two electrodes. One example of a machine by which this printing can be carried out is described in U.S. Pat. No. 4640188. The machine described in this patent specification can be used only for printing in a single color. There are several problems in printing in more than one color, such as, for example, ensuring accurate registration of the colors on a curved surface and of being able to carry out the printing at sufficiently high speeds to be economical. To date, no one has been able to provide a satisfactory machine capable of printing spark plug insulators reliably in more than one color.